I've often wondered why someone can't figure out a better way to expedite eBay and Craigslist transactions without having to rely entirely on "trust and hope" to ensure the transaction goes off without a hitch.
So far as the tile saw goes, what do you think of the idea of you contacting any professional tile setter in the city where the seller lives and agreeing with the seller that he'll pay $10 to the pro to test the saw, cut a scrap tile with it, make sure it's not making any funny noises, etc. The seller then charges you $10 extra for it if the saw gets a clean bill of health. The seller gives the pro $10 for checking it. The pro checks it and writes down it's serial number. You phone the pro and he gives you either the thumbs up or thumbs down on the saw. If it's a thumbs up, he gives you the serial number of the saw he tested. You buy the saw and pay $10 extra for it and check the serial number of the saw you get sent. That way, if you don't get the same saw the pro checked, then you have an impartial witness who can attest that you got sent a different saw than he tested. So, that if you do take up the matter with Craiglist, you've got the weight of evidence on your side, and Craigslist would probably no longer deal with that seller. Not being able to sell anything else on Craigslist would probably be enough of a sanction that most sellers would wanna keep their nose clean.
You could do a similar thing with the pneumatic nailer by contacting any finish carpenter in the same city as the seller.
What I'm thinking is that internet commerce between individuals is a growing business, and there should be a procedure set up to minimize the opportunity for deceit.